The Relationship between Auditory Sensory Gating and Cognitive Functions on Auditory and Visual Modalities in Primary School Children.

Objectives
Considering the common neurological origins, there is a relationship between the sensory gating and cognitive functions. However, there is no adequate information on this issue. In this study, auditory event-related potentials and the sensory gating performance were assessed in P50, N100 and P200 waves. Besides, their relationship with cognitive performance in auditory and visual modalities was investigated.


Materials & Methods
Nineteen normal primary school students (14 boys) were tested in Tehran, Iran from 2017 to 2018. In the auditory modality, the Persian version of the non-word repetition test and monaural selective auditory attention test (mSAAT) were used for assessment of the working memory and selective attention, respectively. In order to evaluate the visual working memory and visual selective attention, Rey-Osterrieth complex figure, selective and divided attention test were used, respectively. A 32-channel EEG system was used for electrophysiological assessment.


Results
The P50 sensory gating was negatively correlated with the visual selective attention (P=0.034, r=-0.49) and N100 sensory gating was negatively correlated with the auditory working memory (P=0.043, r=-0.48) as well as visual selective attention (P=0.039, r=-0.47). For P200, there was a significant negative relationship with auditory selective attention in the right ear (P=0.034, r=-0.49).


Conclusion
Sensory gating in children is not a modality-specific phenomenon. Sensory gating in a modality could be associated with cognitive functions in other modalities.


Introduction
With presentation of a transient acoustic stimulus (S1) to a normal person, a positive auditory eventrelated potential (ERP) can be detected in the frontocentral region of the skull surface within a time interval of about 50 milliseconds (ms) called P50. If a similar acoustic stimulus (S2) is provided within a short time after the first transient acoustic stimulus, the responded evoked potential it is smaller and hence is inhibited or gated. Reduction of the evoked response to S2 represents the sensory gating performance called P50 sensory gating response (1). In other words, the ability of the brain networks to control response to irrelevant environmental stimuli is called sensory gating. This mechanism protects the brain from the overflow of the information (2). The sensory gating ratio can be defined as the ratio of S2 response amplitude to S1 response amplitude multiplied by 100 (S2/S1*100).
Lower ratios reflect better gating capability and stronger reduction of response to irrelevant stimuli.
It represents a precautious inhibitory filter mainly performed by a network including auditory and prefrontal cortices (3).
The prefrontal cortex has several functions. In addition to sensory gating, prefrontal cortex plays an important role in working memory functions and can modulate sensory processing of the brain in regions related to selective attention (4,5).
Considering the common neurological origin and because inhibition of unnecessary input is one of the prerequisites for efficient cognitive processing, including selective attention and working memory (6), there is a relationship between the sensory gating and cognitive functions. Accordingly, sensory gating can improve cognitive abilities through influencing attention and working memory (7). Individuals with higher working memory capacity have a higher ability to maintain selective attention (8). Their performance is also less affected by auditory distraction during visualverbal and auditory-verbal tasks (9,10). In this way, working memory can affect sensory gating in the visual and auditory modalities. However, there are inconsistent reports in studies researched on the potential relationship between cognitive functions and preattentive phase of sensory input processing like P50 gating. For example, relations have been reported between P50 gating and attention, memory and learning (6,11). In contrast, there are studies that do not confirm the existence of such a connection (12,13). Multisensory interactions in auditory cortex have been already identified. Thus, visual input could affect auditory processing (14).
However, how gating function in one modality is related to the cognitive performance in another modality is not well understood.
In addition to the P50, the N100 and P200 waves recorded at a later time window can also represent the sensory gating characteristics (15,16). N100 and P200 sensory gating could reflect different mechanisms than those reflected by P50 gating (16).
These waves represent a triggering of attention or allocation of attention (17). Study on the sensory gating performance at P50, N100 and P200 potentials can represent biological infrastructures that maintain the integrity of cognitive function by preventing the entry of unrelated information to higher processing stages (7). However, less work has been done on sensory gating performance at processing levels after P50 wave. Among the few existing studies on adults, some have pointed to the relationship between cognitive functions and N100 and P200 gating (7,16). Limited information is available on the sensory gating performance in children.
Iran J Child Neurol. Autumn 2019 Vol. 13 No. 4 Given the theoretical importance of sensory gating in preserving the integrity of cognitive functions and normal development of children, we aimed to examine the relationship between auditory sensory gating at P50, N100 and P200 waves and auditory/ visual selective attention and working memory abilities.

Subjects
This cross-sectional study was performed on 19 normal primary school students (14 boys) with a mean age of 9.47 ± 0.71 years. They were selected from the schools on districts 3, 5 and 14 of Tehran and its validity and reliability has been determined (19).

Rey-Osterrieth complex figure test (RCFT)
was used to evaluate the performance of visual working memory in children (20). In this test, the subjects were instructed once to draw the RCFT In this test, in the beginning, two target images were presented to the children so that they became familiar with the test objective. During the test, different images were presented at the center of the monitor with a duration of 250 ms and an interstimulus interval (ISI) of 1000 ms. Participants were required to press the 'space' key whenever they saw any of the target images.

Electrophysiological assessment
For ERP recordings, subjects were seated on a comfortable chair in a sound-attenuated and dimly light room. They were asked to look at a monitor that was playing a silent animated movie in a distance of 100 cm. Free field audio stimuli were presented at 70 decibels A through loudspeakers placed next to the left and right sides to 85 ms was defined as P50. For N100 and P200 analysis, data were low-pass filtered at 35 Hz and data epoching window was -100 to +400 ms from stimulus onset point. The largest negative wave in the latency range of 90 to 160 ms was defined as N100 and the largest positive wave in the latency range of 140 to 250 ms was defined as P200 (7). The epochs were baseline-corrected concerning the mean voltage of the 100 ms pre-stimulus period.
Epochs containing artifacts greater than or equal to 75 µV were rejected (25). If any response was not observed to the S2, it was considered as complete inhibition of response and its amplitude value was assigned as 0.01 µV in the statistical analysis (27). For better demonstration of the results, we performed a grand average to all ERPs. To do so, the ERP waveforms for the separate individuals were simply summed together and then divided by the number of individuals.

Statistics
The test results were analyzed using SPSS (ver. ERPs for S1 and S2 at Cz is shown in Figure 1.

Discussion
In the present study, the relationship between working memory and selective attention in the visual and auditory modalities was examined.
There was a relatively significant relationship between visual selection and auditory working memory in children.
Working memory capacity is said to be a tool for measuring cognitive differences between individuals. This association can be attributed to individual differences in the ability to control attention (8,28). However, little is known on the relationship between these cognitive functions in different modalities. One of the first evidence was provided by investigating the generality of attention control mechanisms associated with working memory (29), which showed a link between auditory attention and visual working memory. Attention and working memory might be considered as overlapping constructs (5). The amount of visual information that a person can store Figure 1. The grand average ERPs for S1 and S2 at Cz Figure 1. The grand average ERPs for S1 and S2 at Cz

Discussion
In the present study, the relationship between working memory and selective attention in the visual and auditory modalities was examined. There was a relatively significant relationship between visual selection and auditory working memory in children.
Working memory capacity is said to be a tool for measuring cognitive differences between individuals. This association can be attributed to individual differences in the ability to control attention (8,28). However, little is known on the relationship between these cognitive functions in different modalities. One of the first evidence was provided by investigating the generality of attention control mechanisms in the visual working memory is predictive of how much that person is able to focus his/her hearing on a particular sound (29). The finding of the present study together with previous reports, suggests supra-modal attention networks that control the flow of information into working memory. This can broaden one's knowledge on the relationship between cognitive function in different modalities, as this relationship is present at early school years.
However, this relationship can become stronger or undergoes some changes because of maturation during adulthood, which needs to be studied.
In the present study, investigation on the relationship between ERPs and cognitive assessments showed that auditory working memory had a negative correlation with amplitude and latency of P50 and N100. This means that in individuals with better performance at working memory task, ERPs were recorded earlier and with smaller amplitude. Higher working memory capacity is related to smaller N100 amplitude and these individuals have more ability Our findings showed that gating in the P50 wave was sensitive to selective attention and smaller ratios were seen in people who had better performance.
The attention model (39)  The results of our study showed that the N100 sensory gating ratio was significantly smaller in children with better performance on visual selective attention. Such a finding was also obtained for the auditory working memory. Generally, N100 and its sensory gating has been linked to the ability of selective attention and considered as a trigger to allocate attention (7,17,41). However, in the present study, in addition to selective attention, this relationship was also observed in working memory. Although a clear relationship has been reported between working memory capacity, attention and N100 wave amplitude (42), to the best of our knowledge, there is no available report on the direct connection between N100 sensory gating and working memory in children.
Interpretation of the findings of the present study in the light of previous studies seems difficult. One of the reasons for the difference in the results of the current and that of previous studies might be the study population. Because maturity of the N100 and its biological substructures is slow, it continues until early adulthood (43). Additionally, to record a reliable N100 wave in children under the age of 10, the ISI must be at least 1000 ms or longer (44). Since this ISI value cannot be used in the stimulation pattern associated with sensory gating response, the interpretation of these findings on N100 sensory gating in children is not yet clear.
Sensory gating in the P200 wave had a significant relationship with auditory selective attention. The P200 is one of the earliest signs of a conscious perception of the acoustic stimulus, as well as an early sign of allocation of attention (17).
Therefore, the sensory gating in P200 wave will also be associated with attention functions. In this study, such a relationship was observed as expected. Considering the language base of the auditory attention test in the present study, in later waves, the sensory gating will be associated with selective attention performance. However, this connection was seen only in the right ear. Given the strong relationship between the right ear with the left hemisphere of the brain and its role in the Haghan: Analyzing the results.

Conflict of interest
The authors declare that there is no conflict of interests.